Oven door latching system



Oct. 31,1967

CGETMAN OVEN DOOR LATCHING SYSTEM Original Filed Nov. 14, 1963 3Sheets-Sheet 1 INVENTOR. CLARE NC E GEZTMAN MM oz. m

HAS ATTORNEY Oct. 31, 1967 c. GETMAN 3,350,542

OVEN DOOR LATCHING SYSTEM Original Filed Nov. 14, 19 63 3 Sheets-Sheet 2INVENTOR. CLAREJUC E GETMAN H ATTORN EY United States Patent Claims.(Cl. 219-412 ABSTRACT OF THE DISCLOSURE A heated cavity such as a bakingand broiling oven or the like, with an access door that is adapted to belocked shut by a manual door latching means. There is also a lockingmeans for holding the door latching means against movement. A solenoidis furnished that is capable of overriding the locking means so that thedoor latching means may be operated. The solenoid is controlled by acircuit with a momentary switch means and a temperature responsiveswitch means that is in heat transfer relation with the heated cavityand is open-circuited at a predetermined critical temperature and above.An indicator light is in cooperation with the temperature responsiveswitch means to be energized when the switch means is open-circuited soas to tell the housewife that the oven interior is inaccessible when thelight is lit.

This present application is a continuation application of my applicationSer. No. 323,809, filed Nov. 14, 1963 and now abandoned. As stated inthe Barber Patent No. 3,313,918 which issued on Apr. 11, 1967 on anapplication Ser. No. 387,439 filed Aug. 4, 1964, the subject of theparent application Ser. No. 323,809 and thereby of this application is alater version of the Barber invention incorporating the differentcombinations therein described and claimed.

The present invention relates to a locking means for a door latchingmechanism and particularly for a door of a high temperature domesticcooking oven of the type having an automatic heat cleaning cycle such asis described and claimed in the copending patent of Bohdan Hurko, No.3,121,158 which was filed on Dec. 13, 1962 as a continuation-in-part ofan earlier application Ser. No. 27,926 that was filed on May 9, 1960 andis now abandoned. Both this patent and application were assigned to theGeneral Electric Company, the assignee of the present invention.

Such an oven would have the normal cooking functions of baking andbroiling within a temperature range between about 150 F. and 550 F. aswell as a heat cleaning operation where the temperature is raised to amaximum somewhere between about 750 F. and about 950 F. for removing thefood soil and grease spatter that accumulates on the walls of the ovenliner during normal cooking. Such a reaction may be characterized by theterm pyrolysis which means the chemical decomposition of matter by theapplication of heat.

Undoubtedly, the major annoyance in using an oven for cooking is thedifi'iculty encountered in keeping the on the hot oven surfaces duringnormal A door operating control eyes if the directions for use are notfollowed verbatim.

Once the principle of automatic heat cleaning of a domestic oven wasperfected by the method of pyrolysis many different systems of applyingthe heat and controlling the cleaning operation were devised to obtainthe desired result. To gain the maximum reliability, standard componentswere used where possible to take advantage of the years of engineeringdevelopment and know-how gained by working with the components, and theywere arranged in fail-safe combinations so that after years oftrouble-free usage of the oven any failure of the component would notconstitute a safety hazard. Instead, the failure of these componentswould render inoperative the heating circuit or function in which thecomponent operates.

The present invention is concerned with means for insuring that the ovendoor is both closed and locked before the heat cleaning cycle can beinitiated, as well as to insure that the oven door cannot be unlocked aslong as the oven temperature is above the maximum normal cookingtemperautre.

The principal object of the present invention, there fore, is to providea locking means for the latching mechanism of a door of a hightemperature oven Where said means becomes effective when the oventemperature rises above normal cooking temperatures with additionalmeans to assure that the locking means cannot be deactivated unless theoven temperature has returned to Within the maximum cooking temperaturerange of about 550 F. and below.

A further object of the present invention is to provide electricalcontrols for a high temperature oven to insure first that the oven dooris closed before the high temperature operation can be initiated, aswell as to insure that the oven door is also locked, and thirdly toinsure that once the oven temperature rises above the maximum normalcooking temperatures that the oven door may not be unlocked, and finallyto provide an indicating means to convey to the housewife theinformation of the temperature within the oven as being within eitherthe normal cooking or the high temperature self-cleaning range.

The present invention, in accordance with one form thereof, is embodiedin a high temperature domestic oven which may be heated either byelectricity or gas. As in standard ovens, the oven cavity is formed byan insulated box-like oven liner and an access door. A door latchingmechanism is provided to hold the door in a closed position during aheat cleaning cycle. A suitable automatic locking means is combined withthe door latching mechanism so as to lock this mechanism in its closedposition. circuit is used to de-activate the locking means at will,depending on whether the operating temperature of the oven is within thenormal cooking temperature range, and enable the movement of the doorlatching mechanism. This control circuit includes an electroresponsivemeans capable of de-activating the locking means. This electroresponsivemeans is electrically connected in series with a normally-closed thermalswitch means that is located in heat transfer relation with the heatedoven cavity. Also, there is a manual switch controller to enable theenergization of the electroresponsive means. The thermal switch means iscalibrated to become open-circuited Whenever the cavity temperaturereaches above about 575 F. thereby rendering the electroresponsive meansincapable of operation. Further modifications include first and secondswitch means connected in series with a biasing resistor that cooperateswith a variableresistance temperature sensor in the thermostatic controlcircuit that has a high positive temperature coefficient of resistances.The first switch means is adapted to be closed automatically when theoven door is closed, and the secnd switch means is adapted to be closedautomatically when the oven door is held closed by the door latchingmechanism, thereby insuring the sealing of the oven door before the hightemperature heat cleaning cycle can be initiated.

My invention will be better understood from the following descriptiontaken in conjunction with the accompanying drawings and its scope willbe pointed out in the appended claims.

FIGURE 1 is a left side elevational view of a freestanding electricrange with parts broken away and some in cross-section to show the mainelements of an oven having an automatic heat cleaning feature thatembodies the present invention;

FIGURE 2 is a fragmentary front elevational view of a range showing theupper portion thereof and mainly the relationship between the oven door,the door latching mechanism, the cooktop and the control panel of therange;

FIGURE 3 is a fragmentary plan view taken on the line 33 of FIGURE 1 toshow the nature of both the door latching means and the means forlocking the door latching means during the high temperature heatcleaning operation;

FIGURE 4 is a diagram of both the power and control circuits for theheating system of the oven of the present invention;

FIGURE 5 is a fragmentary right side cross-sectional elevational view ofthe back portion of the door latching means taken on the line 55 ofFIGURE 3 showing the solenoid-operated locking means for the latchingmechanism as well as the positions of a latch switch and a temperaturesensor switch controller that are included in the temperature controlcircuit. This view is taken on the line 5-5 of FIGURE 3.

Turning now to a consideration of the drawings, and in particular toFIGURE 1, there is shown for illustrative purposes a free-standingelectric range having a top cooking surface or cooktop 13 with aplurality of surface heating elements 12, an oven cavity 13 formed by aboxlike oven liner 14 and a front-opening drop door 15. The oven cavity13 is supplied with the two standard oven heating elements; namely, alower baking element 16 and an upper broiling element 17. A thirdheating element has been added adjacent the oven door to replenish theheat lost in this area and thereby retain generally uniform oven walltemperatures. This third heater is identified as a mullion or perimeterheater 18 that is wrapped around the outside of the oven liner; forexample, in a manner that is taught by the Newell Patent 3,017,488 whichis assigned to the General Electric Company, the assignee of the presentinvention.

The control of the surface heating elements 12 is obtained by selectorswitches 20 which are illustrated as multiple pushbutton switchesarranged in pairs along the opposite side arms of the cooktop 11 to beoriented with the particular heating element that is being controlledthereby. In addition, the range is provided with a backsplash 21 that isvertically disposed along the back edge of the cooktop 11 and providedwith an instrument or control panel 22 as is best seen in FIGURE 2. Thiscontrol panel contains most of the remaining controls for the surfaceheating elements 12 as well as for the oven compartment. Such a controlpanel would ordinarily include an oven selector switch 23, an oventhermostat or temperature responder 24, an automatic surface unitcontrol (not shown), a sequence timer 25 and suitable indicator lights121 and 122 to show when any one of the heating elements ie energized.

Other structural features that might be mentioned by name would be theouter range body or cabinet 27 which has an appearance finish ofporcelain enamel or the like on the outer surface, and which serves asthe superstructure that supports and encloses the various components ofthe range. Sandwiched between the oven liner 14 and the range body orcabinet 27 is an extra thick blanket of thermal insulating material suchas fiber glass or the like. The amount of insulation being used has beenincreased over the amount of insulation for standard ovens because ofthe high operating temperatures encountered during the heat cleaningoperation which will reach a maximum oven air temperature somewherebetween about 750 F. and about 950 F. Another component shown is an aircirculating fan 30 located in the bottom portion or drawer area of therange adjacent the back wall thereof. This fan serves to draw relativelycool room air into the range body 27 through the back of thebacksplasher 21 and down a vertical duct or wiring channel 31 at theback of the range and into the bottom portion of the range where the airrises up suitable ducts (not shown) built into the opposite side wallsof the oven and the air is discharged under the cooktop 11 to beexhausted through openings in and around the surface heating elements12.

During the heat cleaning operation water vapor, free carbon, soot,carbon monoxide gases and other products of combustion are formed andthese are treated before they "are returned to the kitchen atmosphere. Acatalytic smoke eliminator 34 is positioned in an oven vent opening 35to serve as an oxidation and exhaust means for the oven. This catalyticsmoke eliminator is of the type that is taught in the Welch Patent2,900,483 which is assigned to the General Electric Company, theassignee of the present invention. Such a smoke, odor and vaporeliminating device includes a heating means in cooperation with acatalytic platinum surface such as a wire screen that is heated to atemperature of about 1300 F. and tends to consume the smoke, odors andvapors emanating from the oven cavity, so that the oven exhaust air istreated in the manner that is best described in the aforementioned Hurkoapplication Ser. No. 244,493 before being expelled into the kitchen.

It has been found necessary to provide a latching means for the ovendoor 15 to insure that the oven door is closed and cannot be openedwhile the oven is being operated during a heat cleaning cycle. Asuitable door latching mechanism is identified as 37 in FIGURES l and 3,although it is best taught and claimed in the copending patent of thepresent applicant, Clarence Getman, No. 3,189,375 which was filed on May1, 1963 and is assigned to the General Electric Company, the assignee ofthe present invention. Accordingly, only brief mention will be made hereof this mechanism as it does not form part of the present invention. Thelatching mechanism includes a manually operable handle lever 38 whichextends through an elongated slot 39 in the front edge of the cooktop 11of the range in a position just above and parallel to the top edge ofthe oven door 15 as is best seen in FIGURES 1 and 2. Referring to FIGURE3, the handle lever 38 is pivotally supported within a channel-shapedbracket 40 about the pivotal axis 41. The pivoted end of the handlelever 38 also has a channel formation 42 which fits snugly into thechannel-shaped bracket 40 to provide a pair of double pivot means ortrunnions so as to gain stability as the handle lever is moved within ahorizontal plane through an angle of about 60, starting from the openposition of FIGURE 3 to a closed position. The channel braket 40includes a cam-shaped slot 43 in its lower flange cooperating with acam-shaped slot 44 in the lower flange of the channel formation 42 ofthe handle lever 38.

Next, there is a latching bolt 45 which is pivotally actuated by severalpin and slot connections between a recessed or hidden position as shownin FIGURE 3 to a latching position where the bolt is generallyperpendicular to the front wall of the oven and in mating engagementwith a keeper (not shown) within the oven door 15. There is a fixed pin46 that cooperates with a slot 46' in the central portion of thelatching bolt 45. The innermost end of the latching bolt 45 is providedwith a follower pin 47 which operates within bolt cam slots 43 and 44 ofthe bracket 40 and the channel formation 42 of the bandle lever 38respectively so as to obtain the proper action. It should suflice tosummarize that the door latching mechanism 37 includes a pivoted handlelever 38, a fixed mounting bracket 40 and a pivoted latching bolt 45 formaking engagement with the oven door 15. If more details of thismechanism are desired they can be obtained from the previously-mentionedGetman application which is copending herewith.

The description given above has been for the purpose of setting thestage and explaining the environment and utility for the presentinvention. Associated with the door latching means 37 is asolenoid-operated locking means 48 as is best seen in FIGURES 3 and 5for locking the door latching mechanism 37 in both the open and closedpositions. The purpose of locking the door latching mechanism 37 in itsopen position is to insure that it cannot be thrown to the closedposition inadvertently, while it is lock-ed in the closed position toinsure that the door cannot be unlocked and the door opened during anypart of a high temperature heat cleaning operation. Looking at FIGURE 3,the locking mechanism 48 is provided with an elongated upturnedchannel-shaped support bracket 49 that extends from the front to theback of the range and is made integral with the mounting bracket 40 ofthe door latching mechanism 37. The other end of the support bracket 49terminates within the cooling duct or wiring channel 31 at the back ofthe oven.

The main purpose for locating the locking mechanism 48 at a distanceremote from the door latching mechanism 37 and the front of the oven isto remove the locking mechanism 48 from the high temperature areas ofthe range and to place it within the stream of relatively cool room airthat is drawn into the range by the action of the ventilating fan 30, aswas mentioned previously. Movably mounted within the support bracket 49is a connecting rod 50 which is joined at its front end with the handlelever 38 of the door latching mechanism as at pivot point 51.Accordingly, as the handle lever 38 is shifted from its open to itsclosed position the connecting rod 50 will reciprocate within thesupport bracket 49 through a distance of about one inch.

Now turning to FIGURE 5, the back end of the locking mechanism 48 isprovided with a solenoid-operated pivoted bolt 53 that makes engagementwith the connecting rod 50 in both of its extreme positions, therebyrequiring the movement of the pivoted bolt before the connecting rod andhence the handle lever 38 can be moved. The bolt 53 is pivoted about ahorizontal axis 54, and it is motivated by the solenoid 55 that has avertically acting armature 56 pivotally connected to the bolt as at 57.The solenoid 55 is fastened to a hat-shaped channel member or bracket 58as can best be pictured in FIGURE 3, said bracket being utilized tomount the combined door latching mechanism 37 and door locking mechanism48 to the range body 27. The pivoted bolt 53 is normally biased in adownward direction by a tension spring 60. The other end of the bolt hasa down-turned finger portion 61 that cooperates with both the beck edge62 of the connecting rod and a slot 63 closely spaced therefrom. Lookingat FIGURE 5, the connecting rod 50 is shown in its position when thehandle lever 38 is in the open position of FIGURE 3. The finger 61 ofthe pivoted bolt 53 is lodged in the slot 63 of the connecting rod sothat the rod cannot be moved until the solenoid 55 is energized to liftthe bolt out of the slot against the downward force exerted by thetension spring 60. When the handle lever 38 is in its closed position,the finger 61 of the bolt 63 is engaged behind the innermost end 62 ofthe connecting rod so that the door latching mechanism cannot be openeduntil the solenoid 55 is operated to lift the bolt as heretofore.

The pivoted bolt 53 also includes a second down-turned finger 64 whichextends through a suitable slot in both the connecting rod 50 and thesupport bracket 49. This down-turned finger 64 serves to guide themovement of the connecting rod 50 so as to provide smooth operationthereof. A temperature senser switch controller 65 is positioned belowthe finger 61 of the pivoted bolt 53, and this switch has a button 66that is engaged by the finger 61 when the door latch mechanism is closedand the solenoid 55 is de-energized for reasons which will better beunderstood hereinafter. A second switch member 67 is mounted to thebracket 58, and it has a switch button 68 that is adapted to be engagedby a tab 69 that is attached to the conecting rod 50 as is best seen inFIGURE 3. This latch switch 67 is a single-pole double-throw switchserving as part of the protector means for the oven as will also befully explained hereinafter.

Turning now to a consideration of the circuit diagram of FIGURE 4, theelectric range of the present invention is provided with an electricalservice of 3-wire Edison source of power nominally of 240 volts, singlephase, 60 cycle A.C. which is usually available in the average residencehaving adequate wiring. This voltage source has a pair of line wires L1and L2 and a grounded neutral conductor N for supplying the sequencetimer 25, the oven selector switch 23 and the load characterized by thethree heating elements; namely, the baking element 16, the broilingelement 17, and the mullion heater 18. There is also a low voltagetemperature control circuit for the oven thermostat 24 which is fed by astep-down transformer 70 for providing about 12 volts in a circuit thatincludes the thermostat 24, a variable-resistance temperature sensor 71,a biasing resistor 72, the operation of which will be explainedhereinafter, the sensor switch controller 65 that was mentionedpreviously and a normally open door-operated switch 73 which will beclosed when the oven door is closed In addition to the power circuit andthe low voltage temperature control circuit, there is a door latchcontrol circuit that includes the following elements: the connecting rod50 of the door latch mechanism 37, the pivoted bolt 53 that is operatedby the solenoid 55, the single pole, double throw latch switch 67 thatis operated by the movement of the door latching mechanism, and the fanmotor 30 for circulating room air between the range body and theinsulated oven structure. Other elements will be described during adetailed description of the circuit operation.

Means must also be provided to prevent the operation of the doorlatching mechanism 37 once the temperature within the oven cavity risesabove the maximum normal cooking temperature of about 550 F. For thispurpose a normally-closed thermal switch 75 is arranged in series withthe solenoid 55 so that as soon as the oven temperature rises above themaximum normal cooking temperatures, the thermal switch 75 will open andthe solenoid 55 is thereby de-energized so that the door latch mechanismcannot be moved until the oven temperature returns to the normal cookingtemperature range. More details of the interrelation between themechanism and the locking means therefor will be given after detaileddescriptions of the power circuit and the temperature control circuit.

The oven selector switch 23 is provided with four line terminals orpoles N, L1, L2, and T1 for connection with the lead wires from thepower supply. Terminal T1 is for use by the sequence timer 25 as will beexplained later. The selector switch 23 also has four load terminalsidentified as A, B, C and D as well as 8 sets of switch contacts -87inclusive. These switch contacts are each labeled with the operationthat takes place when the respective contacts are closed. For example,during a baking operation, contacts 82, 84 and 86 are closed. During abroiling operation contacts 80 and 86 are closed, while during a timedbaking operation contacts 82, 84 and 87 are closed. Finally, during theheat cleaning operation contacts 81, 83, and 87 are closed.

The baking circuit has the baking element 16 connected directly acrossfull voltage of 240 volts from line L1 to L2, while at the same time thebroiling element 17 is in series with the mullion heater 18 in a circuitthat parallels the baking element. This can be better understood bytracing the circuit as follows: for the baking element 16, the circuitis from line terminal L1, through switch contacts 82 to load terminal B,and then by lead 90 through baking element 16, by lead 91 through theclosed thermostat contacts 92, and by lead 93 back to line L2. As forthe broiling element 17 and mullion heater 18, the circuit is asfollows: from line terminal L1 by internal switch lead 95 to switchcontacts 84 to load terminal C and then by lead 96 through the mullionheater 18 and then in series with the broiling element 17 by lead 97,and then by lead 98 and leads 91 and 93 back to line L2 through thethermostat contacts 92.

The broiling circuit has the broiling element 17 as the only elementthat is energized, and it is connected across the 240 volts of lines L1and L2. The circuit is from line terminal L1 through internal switchlead 99 to switch contacts 80 and then to load terminal A. Then, byleads 100 and 101 to the broiling element 17 and then back to the lineL2 through leads 98, 91 and 93 as well as through the thermostatcontacts 92.

Next to be considered is the heat cleaning circuit where all threeheating elements 16, 17 and 18 are connected in parallel across one-halfline voltage of 120 volts from neutral conductor N to line L2. Forexample, the circuit for the mullion heater 18 is from line terminal Nthrough switch contacts 81 to load terminal A, and by leads 100 and 97to mullion heater 18, and then by lead 96 to load terminal C to switchcontacts 85 to line terminal L2 and then by lead 124 through thethermostat contacts 92, and then by lead 93 to line L2. In a similarmanner, the circuit for the broiling element 17 is from load terminal Athrough leads 100 and 101 through broiling element 17 and back to lineL2 through leads 91 and 93 and closed thermostat contacts 92. Lastly,the baking element circuit is from line terminal N through internalswitch lead 103 through switch contacts 83, and then by lead 90 throughbaking element 16, and then back to line L2 through leads 91 and 93 andthrough thermostat contacts 92.

As mentioned previously, the power circuit is provided with a singlesequence timer 25, for timing both the baking operation and the heatcleaning operation. An example of a suitable timer is that disclosed inthe Zagorski Patent 3,038,041 which is assigned to the General ElectricCompany, assignee of the present invention. This type of timer wouldinclude an electric clock mechanism 105, a start dial 106 and a stopdial 107 so that the timer could be set for an automatic closing orstarting of the power circuit at a given starting time set on the dial106, and the circuit would be opened automatically at a given stop timeset by the dial 107. This timer mechanism must be electricallyenergized, and it is shown as being connected across line L1 and neutralconductor N by leads 108 and 109, respectively. The timer 25 has asingle pole switch cont act 110 that is interposed in the line L1 aheadof the line terminal T1. Accordingly, to bring the sequence timer 25into the power circuit during the time baking or heat cleaningoperations, the switch contacts 87 must be closed in place of the switchcontacts 86 which are closed only during the baking and broilingoperations.

Turning now to a consideration of the temperature control device orthermostat 24, it is of the general type that is taught in the UnitedStates patent to Harry 1. Baker, 2,962,575. Such devices over the yearshave proved to be quite satisfactory for use as oven thermostats fornormal cooking temperatures, but none of them have been commerciallyavailable at a reasonable price to extend over the wide temperaturerange that would cover in addition to the normal cooking temperatures,the heat cleaning temperatures between about 750 F. and about 950 F.,and still have the necessary degree of accuracy throughout the entirerange of temperatures. An improvement has been made in this controlsystem by the introduction of a biasing resistor 72 that is shuntedacross a variableresistance temperature sensor 71 (located within theoven cavity) when the heat cleaning temperature range is desired. Thisbiasing resistor 72 functions to shift the control point of the circuitso as to be able to obtain accurate results for the complete range oftemperatures. The thermostat 24 is a manually settable responder thatmay include a voltage regulating relay (not shown) so that the sensor 71varies the effective output voltage of the relay in accordance with thesensed temperature within the oven cavity regardless of variations inthe line voltage. The thermostat may also include a responder relay (notshown) that receives the effective output voltage of the voltageregulator and controls the output relay 112 that includes the thermostatcontacts 92, which were mentioned previously as being the single poleswitching means for controlling the temperature within the oven cavity.See the Welch Patent No. 3,122,626 for more information in this regard.

Several precautionary measures are built into this temperature controlcircuit to insure that the oven door 15 is closed and the door latchingmechanism 37 is moved to its closed position before the heat cleaningoperation can be initiated. Connected in series with the biasingresistor 72 is both a door switch 73 that is closed when the door isclosed and a temperature sensor switch controller 65 that is closed whenthe door latching mechanism is closed. This door switch 73 is notillustrated in the assembly views of FIGURES 13, but only in the circuitdiagram of FIGURE 4. However, those skilled in this art will understandthat the switch is to be mounted on the front face of the oven adjacentthe door opening and within the outlines of the door so that when thedoor is closed the door switch 73 is contacted by the door and therebyclosed. Suitable leads 114, 115, 116 and 117 connect the biasingresistor 72 in parallel with the temperature sensor 71 and connect thedoor switch 73 and sensor switch 65 in series with the biasing resistor72 when these switches are closed.

Whenever the oven selector switch 23 is set in an energizing position,as distinguished from an OFF position, a circuit is completed throughthe step-down transformer 70 by means of load terminal D and leads 119and 120 which is in turn connected back to the neutral conductor N.Connected in a parallel circuit across the primary of the transformer 70is an oven indicator light 121 as well 'as the smoke eliminator 34 whichwas mentioned previously. This means that whenever the power circuit toany one of the heating elements 16-18 is completed the transformer 70and the low voltage temperature control circuit that includes thethermostat 24 will be energized as will the indicator light 121 andsmoke eliminator 34. Moreover, a cycling pilot light 122 is connected inthe power circuit so as to be energized whenever the thermostat contacts92 are closed. This connection is made by a lead 123 to the loadterminal D and by lead 124 to the thermostat contacts 92.

Finally, there is an electrical control circuit for the locking means 48for the door latching mechanism 37. As explained previously, it is notpossible to move the door latching mechanism by throwing the handlelever 38 until the pivoted bolt 53 is withdrawn from engagement with theconnecting rod 50 by operating the solenoid 55. This solenoid isconnected in a series circuit with a momentary pushbutton switch 126that is in turn connected across line L1 and neutral conductor N bymeans of lead 127, 128, 129, 130 and the return lead 120. It is alsoimportant to insure that the door latching mechanism 37 cannot beopened, once it is closed after the oven temperature-s have reached intothe heat cleaning range above the maximum normal cooking temperaturerange of about 550 F. This feature is provided by a normally-closedbimetallic or differential expansion switch 75 located in series withthe solenoid 55 between leads 128 and 129. This thermostat is calibratedto be normally closed at all temperatures below the maximum cookingtemperature range of about 550 F. Once the oven temperature rises abovethis maximum the thermal switch 75 would be opened and the solenoid 55would thereby be rendered inoperative in spite of any subsequent closingof the momentary switch 126.

It is also well to have a visual indication when the oven is operatingin its heat cleaning cycle to inform the housewife that the doorlatching mechanism 37 cannot and should not be opened. This informationis supplied by a lock light or neon glow lamp 132 that is shunted acrossthe thermal switch 75. This lock light 132 is energized whenever thedoor latching mechanism 37 has been closed which, in turn, causes thetab 69 on the connecting rod 50 of the latching mechanism 37 to shiftforward and engage the button 68 of the single-pole double-throw switch67 to complete a circuit between line L1 and neutral conductor N whenthe thermal switch 75 has been opened by a high temperature condition.This circuit may be traced from line L1 to lead 127 and lead 134 to thelatch switch 67 and then by lead 135 through a current limiting resistor136 which is connected in series with the parallel circuit of the locklight 132 and the thermal switch 75 as 'well as with the solenoid 55.The purpose of the resistor 136 is to allow the passage of very littlecurrent when the door is latched so that only the lock light 132 isenergized and there is not enough current available to operate thesolenoid 55. This is done so that it is not necessary to depress themanual switch 126 in order to energize the lamp 132. In the specificembodiment illustrated, this resistor has a rating of about 5,000 ohms.Thus, the closing of the momentary pushbutton switch 126 serves to shortout the resistor 136 thereby actuating the solenoid 55. An alternatecircuit would be to have the resistor 1336 connected in parallel with aseries connection of the momentary switch 126 and the solenoid 55. Thisarrangement is then in series with a parallel circuit comprising on theone hand a neon glow lamp 132 and on the other hand the thermal swi ch75. It should be noticed that the air circulating fan 30 is connected inthis solenoid circuit across L1 and N so as to be energized whenever thedoor latching mechanism 37 is closed.

Mention is also made of the fact that when the latch switch 67 is in itsunlatched position as shown in FIG- URE 4, the switch is connected inseries with the line terminal L1 of the selector switch 23 by means oflead 138. In other words, the line terminal L1 of the selector switch 23is only energized when the door latching mechanism is in its open orunlatched position. This is important to insure that the heat cleaningoperation cannot be initiated when the manual controls are not setproperly. If this were possible, the selector switch 23 might be set ateither its baking or its broiling positions across full line voltage of240 volts and permanent damage could be done to the porcelain enamel ofthe oven liner 14 due to the rapid heat rise. Accordingly, if the doorlatching mechanism is closed when the oven switch is not set at theclean position, the latch switch 67 will disconnect the line L1 from theselector switch thereby deenergizing the power circuit and turning outthe cycling pilot light 122, and the oven indicator light 121, whileleaving only the lock light 132 energized.

Modifications of this invention will occur to those skilled in this arttherefore it is to be understood that this invention is not limited tothe particular embodiments disclosed but that it is intended to coverall modifications which are within the true spirit and scope of thisinvention as claimed.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In a heated cavity formed by an insulated boxlike body and an accessdoor for closing and sealing said cavity, and heating means arranged forconnection to an energy source for raising the temperature within thecavity, and door latching means movable between an open and closedposition, locking means for holding the door latching means againstmovement in its closed position; the improvement comprising anelectroresponsive means capable of over-riding the locking means so thatthe door latching means may be operated, and a normally-closedtemperature responsive switch means 10-. cated in heat transfer relationwith the heated cavity and being in a series electrical circuit with theelectroresponsive means and a momentary contact switch means so thatclosure of the momentary contact switch means will energize theelectroresponsive means and free the door latching means from thelocking means, the rise in temperature within the heated cavity above apredetermined critical temperature serving to open the temperatureresponsive means and thereby de-activate the electroresponsive meansuntil such temperature returns below the critical temperature limit.

2. The invention as recited in claim 1 with the addition of an indicatorlamp means shunted across the temperature responsive switch means, and acurrent limiting resistor connected in series with the lamp means so asto energize the lamp when the temperature responsive switch means isopen circuited by a critical temperature condition although themomentary contact switch means is not closed.

3. In a control circuit for an oven heating system comprising a sourceof electrical energy, a plurality of heating elements connected to theenergy source, and a selector switch cooperating with the heatingelements for obtaining various circuit combinations, a thermostaticcontrol circuit including a variable-resistance temperature sensor, aresponder and an output relay that governs the amount of energy suppliedto the heating element, a biasing resistor capable of being shuntedacross the temperature sensor so as to change the control point of thethermostatic control circuit; the improvement comprising a first and asecond normally-open switch means connected in series with the biasingresistor to insure the closure of these switches before the applicationof the said biasing resistor, the said first switch means being latchingmeans, and locking means for holding the door latching means againstmovement from its closed position, a solenoid operator for overridingthe locking means to enable the operation of the door latching means,said solenoid operator being in a series circuit with a manual switchmeans and a normally-closed thermal switch that is open-circuited at apredetermined critical temperature.

4. A control circuit as recited in claim 3 with the addition of acurrent limiting resistor capable of being shunted around the manualswitch means by a third switch means that is closed by movement of thedoor latching means to a closed position, an indicator lamp shuntedaround the normally closed-thermally operated switch, said lamp beingenergized whenever the door latching means holds the oven door in theclosed position and the oven temperature is above the predeterminedcritical temperature.

5. In a high temperature oven for domestic use comprising a cabinetstructure enclosing a box-like oven liner that 'has an open front thatis adapted to be closed by an access door, where the oven liner and doordefine an oven cooking cavity, means for supplying heat energy into theoven cavity for normal cooking operations between about F. and 550 F. aswell as for a heat cleaning operation between about 750 F. and 950 F.for removing food soil lodged on the walls of the oven cavity, and adoor latching mechanism movable between an open and closed position forholding the door closed during the heat cleaning operation, and aspring-actuated locking means engageable with the door latchingmechanism in its closed position to prevent the movement of the saidmechanism; the improvement comprising a normally-closed thermal switchand a normallyopen switch means, and a door operating circuit includingan electroresponsive means mechanically connected to the said lockingmeans and electrically in series with the normally-closed thermal switchand the normallyopen switch means, the door control circuit beingconnected to a source of electrical energy so that the closure of thesaid switch actuator will energize the electroresponsive means and causeit to disengage the locking means from the door latching mechanism andpermit free movement of the said mechanism, the said thermallyresponsiveswitch being calibrated to be opened before reaching a criticaltemperature rangs so that the door cannot be unlocked when the oventemperature is above a predetermined critical temperature.

6. A high temperature over for domestic use comprising a cabinetstructure enclosing an insulated box-like oven liner that has an openfront that is adapted to be closed by an access door, where the ovenliner and door define a cooking cavity, means for supplying heat energyinto the oven cavity for normal cooking operations between about 150 F.and 550 F. as Well as for a heat cleaning operation between about 750 F.and 950 F. for removing food soil lodged on the walls of the ovencavity, and door locking means movable between an open and closedposition for holding the door closed during the heat cleaning operation;the invention comprising a solenoid-operated locking member engageablewith the door latching mechanism in both its open and closed positionsto prevent the movement of said mechanism therefrom, and a dooroperating control circuit that includes a solenoid joined to saidlocking member and electrically connected in series with a manual switchcontroller, a normally-closed thermal switch and a source of electricalenergy, whereby the closure of the manual switch controller willenergize the solenoid and serve to release the locking member from thelatching mechanism, the said thermal switch being calibrated to open ata predetermined critical temperature so as to de-activate the doorlatching mechanism when the temperature within the oven cavity isanywhere above the critical temperature.

7. A heated cavity formed by an insulated box-like body and an accessdoor for closing and sealing said cavity, heating element means forconverting an electrical energy source into heat, and a selector switchgoverning the heating element means for obtaining various power circuitscombination from said energy source, a temperature control circuitincluding an electrical variableresistance temperature sensorcooperating with a responder and an output relay means to govern theamount of energy supplied to the heating element means during normalcooking operations of between about 150 F. and 550 F., a biasingresistor connected in a circuit and adapted to be shunted across thesensor so as to shift the control points of the temperature controlcircuit into a high temperature range between about 750 F. and 950 F., anormally-open interlock switch means connected in series with thebiasing resistor to require the closure of the switching in order toenergize said biasing circuit, and door latching means movable betweenan open and closed position, and door latching means movable between anopen and closed position and adapted to hold the door in a closedposition during the high temperature operation, said door latching meansserving to close the interlock switch when the oven door is latched inits closed position, locking means for locking the door latching meansin its closed position; the improvement comprising an electroresponsivemeans capable of de-activating the locking means to free the doorlatching means for operation, and a normally-closed thermal switch meanslocated in heat transfer relation with the heated cavity and in a serieselectrical circuit with the electroresponsive means, said thermal switchmeans being calibrated to become open-circuited before reaching acritical cavity temperature, and an indicator lamp means shunted acrossthe thermal switch means, and a current limiting resistor in series withthe lamp means so as to energize the lamp whenever the temperatureresponsive switch means is open-circuited by a critical temperaturecondition, and momentary contact switch means in series with theelectroresponsive means for energizing the same whenever the thermalswitch means is closed.

8. In a high temperature oven for domestic use as recited in claim 5wherein the said electroresponsive means comprises a solenoid, and anindicator lamp shunted across the normally-closed thermal switch, and acurrent limiting resistor connected in series with the said lamp soas'to energize the lamp when the thermal switch is open circuited by acritical temperature condition.

9. In a household oven having a cavity formed by an insulated box-likebody and an access door for opening and closing said cavity, heatingmeans arranged for connection to an energy source for raising thetemperature within the cavity, door latching means movable to an openand a closed position, and locking means for normally holding the doorlatching means against movement in its closed position; the improvementcomprising an electroresponsive means capable of overriding the lockingmeans so that the door latching means may be operated, temperatureresponsive switch means located in heat transfer relation with theheated cavity, a momentary contact switch means, and circuit meansconnecting said electroresponsive means with said temperature responsiveswitch means and said momentary contact switch means so that closing ofsaid momentary switch means will energize the electroresponsive meansand free the door latching means from the said locking means, the risein temperature within said heated cavity above a predeterminedtemperature serving to actuate the temperature responsive switch meansand thereby render the circuit means incapable of energizing theelectroresponsive means while the temperature in said cavity is abovesaid predetermined temperature, said temperature responsive switch meanspermitting energization of said electroresponsive means when thetemperature in the cavity returns below said predetermined temperature.

10. In a household oven having an insulated box-like body and an accessdoor for opening and closing said cavity, heating means arranged forconnection to said energy source for raising the temperature within thecavity during normal cooking operations of between about F. and about550 F. as well as into a heat cleaning temperature range above about 750F., door latching means movable to an open and a closed position,locking means for normally holding the door latching means againstmovement in its closed position, the improvement comprising anelectroresponsive means capable of releasing the locking means so thatthe door latching means may be operated, and temperature responsivemeans located in heat transfer relation with the heated cavity, amanually operated switch means, and circuit means connecting saidelectroresponsive means with said temperature responsive means and themanually operated switch means so that closing of the manually operatedswitch means will energize the electroresponsive means and free the doorlatching means from the locking means, the rise in temperature withinthe heated cavity above the normal cooking temperature range serving toactuate the temperature responsive switch means and thereby render thecircuit means incapable of energizing the electroresponsive means whilethe temperature in said cavity is above said normal cooking temperatureseven though said manually operated switch means is closed, whereby whenthe temperature in the cavity returns to within the normal cookingtemperature range said temperature responsive means permits energizationof said electroresponsive means.

1 4 References Cited UNITED STATES PATENTS 8/1962 Scott 126-273 3/1964Eigelbach 2927 RICHARD M. WOOD, Primary Examiner. C. L. ALBRITTON,Assistant Examiner,

1. IN A HEATED CAVITY FORMED BY AN INSULATED BOXLIKE BODY AND AN ACCESSDOOR FOR CLOSING AND SEALING SAID CAVITY, AND HEATING MEANS ARRANGED FORCONNECTION TO AN ENERGY SOURCE FOR RAISING THE TEMPERATURE WITHIN THECAVITY, AND DOOR LATCHING MEANS MOVABLE BETWEEN AN OPEN AND CLOSEDPOSITION, LOCKING MEANS FOR HOLDING THE DOOR LATCHING MEANS AGAINSTMOVEMENT IN ITS CLOSED POSITION; THE IMPROVEMENT COMPRISING ANELECTRORESPONSIVE MEANS CAPABLE OF SAID-RIDING THE LOCKING MEANS SO THATTHE DOOR LATCHING MEANS MAY BE OPERATED, AND A NORMALLY-CLOSEDTEMPERATURE RESPONSIVE SWITCH MEANS LOCATED IN HEAT TRANSFER RELATIONWITH THE HEATED CAVITY AND BEING IN A SERIES ELECTRICAL CIRCUIT WITH THEELECTRORESPONSIVE MEANS AND A MOMENTARY CONTACT SWITCH MEANS SO THATCLOSURE OF THE MOMENTARY CONTACT SWITCH MEANS